1. Field of the Invention
The present invention relates to a vehicle antenna and, in particular to an antenna formed by a transparent coating laminated between two glass plies and an electrical connection arrangement for connecting the antenna to a radio or other transmitting/receiving device.
2. Technical Considerations
In the past, the traditional motor vehicle antenna for receiving and transmitting electromagnetic signals was a mast or whip type antenna. Recently there has been a trend towards incorporating the antenna into the vehicle structure. For example, U.S. Pat. Nos. 4,768,037 and 4,849,766 to Anaba, et al. and U.S. Pat. No. 5,355,144 to Walton, et al. disclose a transparent electroconductive coating over a substantial portion of a window and, in particular a vehicle windshield to form an antenna. In designing an antenna system, attention is given to matching the impedance of the system""s components and, in particular matching the impedance of the radio, the antenna and a feed line electrically interconnecting the two components to improve the reception of selected radio signals. One way this issue has been addressed by antenna designers is to design the antenna to have a desired impedance, for example as disclosed in U.S. Pat. Nos. 5,083,135; 5,528,314; and 5,648,758 to Nagey, et al. However, designing an antenna to have a predetermined impedance would require each antenna to be designed specifically for the particular type of radio and feed line used in the particular antenna system, as well as the vehicle into which the antenna is installed.
In order to link the antenna element to an external device, connectors such as wires, braids or tabs have been laminated within the transparency to make electrical contact with an antenna element. However, it has been found that when incorporating these type of connectors between the plies of the laminate, air may be trapped in the laminate in the vicinity of the connector. It is believed that the air entrapment is the result of the connector hindering the de-airing of the laminate during a conventional roll prepress operation. Bubbles formed by the entrapped air detract from the aesthetics of the laminate, as well as increase the possibility of delamination and/or corrosion at or near the connection.
To solve both these problems, a capacitive type connection has been used to electrically interconnect the antenna elements to the feed lines for a radio, e.g. as disclosed in U.S. Pat. No. 5,355,144. More specifically, an electroconductive material is applied on the inner surface of the windshield and is capacitively coupled to a portion of a coating within the windshield that forms an antenna element. The area of the material on the inner surface of the windshield is adjusted to provide the proper capacitance between the antenna coating and the material. However, the presence of the connector material blocks the vision of the vehicle operator. It would be advantageous to provide a connection arrangement which provides the required capacitive performance for the connection while at the same time providing the vehicle operator increased visibility in the vicinity of the connector with minimal distraction.
The present invention provides a transparent antenna including a transparent dielectric substrate, an electroconductive antenna element positioned along a major surface of the substrate, an electroconductive patch capacitively or directly connected to the antenna element, and a connector secured to the patch to permit transfer of signals generated by the antenna element to an electromagnetic energy transmitting and/or receiving device. The patch, is configured to have a visibility coefficient (i.e. a ratio of the non-opaque area to the total area) between 0 and 1. In one particular embodiment of the invention, the antenna element includes one or more transparent, electroconductive coatings positioned between first and second glass plies of a windshield for a motor vehicle and the electroconductive patch is applied to an exposed major surface of the windshield such that it overlays at least a portion of the antenna element and is capacitively coupled to the antenna element.